This invention relates generally to marine engines and, more specifically, to detecting engine exhaust gas pressure in a fuel injected or direct fuel injected engine.
Marine engines typically include a power head, an exhaust housing, and a lower unit. A drive shaft extends from the power head, through the exhaust housing, and into the lower unit. The lower unit includes a gear case, which supports a propeller shaft. One end of the propeller shaft is engaged to the drive shaft, and a propeller is engaged to an opposing end of the shaft.
In order to maintain optimum combustion, as airflow to the cylinders increases, fuel flow to the cylinders also should increase. As airflow to the cylinders decreases, fuel flow to the cylinders also should decrease.
Many variables impact airflow to the cylinders including conditions at the propeller. For example, the depth at which an engine propeller is located in the water impacts air flow through the engine, including an amount of fresh air supplied to the engine cylinders. Fuel flow to the cylinders also is adjusted based on operating parameters such as atmospheric pressure and intake air temperature. An absolute pressure sensor typically is utilized for generating a signal representative of atmospheric pressure, and a temperature sensor typically is located at the engine air intake to generate a signal representative of intake air temperature. The sensors are coupled to, or part of, an electronic control unit (ECU), which samples the signals generated by the sensors and adjusts fuel flow according to the sampled signals.
An additional parameter that has a significant impact on fresh airflow to the engine cylinders is exhaust flow. Specifically, a key parameter governing the exhaust gas flow is the gas pressure within the exhaust system. Known commercial marine engines, however, do not utilize exhaust gas pressure data in controlling the fuel/air ratio in the engine cylinders.
More specifically, and until now, the difficulties and costs associated with measuring such exhaust gas pressure for controlling the fuel/air ratio during engine operations were prohibitive in commercial marine engines. For example, the carbon and soot resulting from the combustion process can collect and block the sensor, preventing it from reading pressure. In addition, exhaust gas from an internal combustion engine contains known corrosive compounds which can damage electrical components.